I think you'll find if you read thru that thread, it has a fair amount of info.
in a nutshell - RAAus is the adminstrative body for issuing the RAAus certs, which restrict you to a 2 seat, single engine plane less than 600 kg, and no access to controlled airspace, and on the RAAus registry. wtih the proper endorsements, that still allows you 1 passenger and access to 95% of the country. CASA adminsters general aviation (GA) and issues the RPL, which is a step on the way to the Private Pilot Licence. It allows more or less the same, but in a VH- registered plane up to 1500 kg, and allows access into controlled airspace.
They are roughly equivalent, but separate. The skills and terminology are (mostly) the same and if you have one, you can easily transfer to get the other (options!)